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05-12-2020, 05:29 PM   #1
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DOT TUNE AF Adjustment

"DOT TUNE" by TESTCAMS on YouTube is a fast, success-oriented solution to AF fine adjustment. All you need is a target and a tripod. Nothing to purchase. No pictures to take and examine. In fact you do not have to take any pictures. I used his procedure strictly by the video and achieved very pleasing AF accuracy results in minutes. Did my KP and two Pentax primes and the 20-40 mm Limited zoom. I could not be happier with the results.

05-12-2020, 05:37 PM   #2
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Discussed in more detail in this thread:
Dot Focus microfocus adjustment - PentaxForums.com
05-13-2020, 12:41 AM   #3
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QuoteOriginally posted by gatorguy Quote
Discussed in more detail in this thread:
Dot Focus microfocus adjustment - PentaxForums.com
Unfortunately the link provided there does not work anymore.
05-13-2020, 03:30 AM   #4
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QuoteOriginally posted by AfterPentax Quote
Unfortunately the link provided there does not work anymore.
The link to the thread? It works, and the discussion is very informative. The direct link to the DOT TUNE video in that thread may not work any longer, dunno. I found it via a web search.

Here's good link
https://www.youtube.com/playlist?list=PL3z1B0ssxKO7-ShMRUfG_oqrk_iB-Ophh

05-13-2020, 03:41 AM - 1 Like   #5
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QuoteOriginally posted by doc58bc Quote
"DOT TUNE" by TESTCAMS on YouTube
Here's the link
I've used it and not only can it be less time consuming, but seems more logical/scientific. It accepts the reality that there is an adjustment range at which a camera will interpret something as "in focus" and sets the fine tune adjustment to the center of that range. The more common method (fastidious test setup, test shots, interpretation of each shot, guessed adjustment; repeat test shots, interpretation of each shot, guessed adjustment; repeat . . .) seems to rely on tireless testing with the hope of stumbling on a representative sample of the camera's AF tolerances to find the acceptable range of adjustment.

---------- Post added 05-13-20 at 06:43 AM ----------

QuoteOriginally posted by doc58bc Quote
"DOT TUNE" by TESTCAMS on YouTube
Here's the link

I've used it and not only can it be less time consuming, but seems more logical/scientific. It accepts the reality that there is an adjustment range at which a camera will interpret something as "in focus" and sets the fine tune adjustment to the center of that range. The more common method (fastidious test setup, test shots, interpretation of each shot, guessed adjustment; repeat test shots, interpretation of each shot, guessed adjustment; repeat . . .) seems to rely on tireless testing with the hope of stumbling on a representative sample of the camera's AF tolerances to find the acceptable range of adjustment.
05-13-2020, 03:58 AM   #6
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The result and the basic technique is not different to any other setup. The workflow may be faster for some, but is not radically different or new - assuming you use some kind of technique other than trial and error on undefined targets.
02-01-2022, 05:53 AM   #7
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I've just got second-hand lens (Sigma 70-200 f2.8) and Dot Tune session showed that 70mm starts focusing at +4 and goes all the way till +10, while 200mm goes completely into opposite direction, starts focusing at -4 and goes all the way to -10.
The ranges do not even overlap?!?

My biggest question is it bad lens, or it happens?

02-01-2022, 06:19 AM - 1 Like   #8
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QuoteOriginally posted by Fila Quote
I've just got second-hand lens (Sigma 70-200 f2.8) and Dot Tune session showed that 70mm starts focusing at +4 and goes all the way till +10, while 200mm goes completely into opposite direction, starts focusing at -4 and goes all the way to -10.
The ranges do not even overlap?!?

My biggest question is it bad lens, or it happens?


Were these tests all at one distance, or, as Pentax suggests, at "a distance 30 to 40 times the lens’s focal length" for each setting?
02-01-2022, 11:13 AM - 1 Like   #9
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QuoteOriginally posted by Fila Quote
I've just got second-hand lens (Sigma 70-200 f2.8) and Dot Tune session showed that 70mm starts focusing at +4 and goes all the way till +10, while 200mm goes completely into opposite direction, starts focusing at -4 and goes all the way to -10.
The ranges do not even overlap?!?

My biggest question is it bad lens, or it happens?
My DFA* differs by 2 steps between 70/135/200 mm which is visible wide open, but OK including dof …. If you did everything correct - make sample images to check - your lens just fails. Call Sigma and complain. Do you have other lens that work as expected?
Check tripod, illumination (avoid artificial light on older Pentax cameras), check target, be aware that the focus point can be larger in reality, …
02-01-2022, 11:29 AM - 1 Like   #10
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QuoteOriginally posted by Fila Quote
My biggest question is it bad lens, or it happens?
I have a couple of zoom lenses that required different AFFA settings on my K-3 II, depending on their focal lengths. For example, for my DA 20-40mm Limited, I found that the optimal AFFA calibration at 20mm was significantly different from that at 30mm and 40mm. The only setting that gave the sharpest autofocus at all focal lengths was AFFA = +2, but only when focused from infinity. So, I would simply preset the focus to infinity before each shot.

On my K-3 Mark III, I was able to find a single AFFA setting for each of my zoom lenses that produces acceptable focus across their focal length ranges.

I have a Sigma 70-200 f/2.8 HSM II, which requires an AFFA setting of -9 on my K-3 II and -7 on my K-3 Mark III. The settings produce acceptable focus at all focal lengths.

- Craig
02-01-2022, 03:41 PM   #11
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Thanks a lot everybody


QuoteOriginally posted by kypfer Quote
Were these tests all at one distance, or, as Pentax suggests, at "a distance 30 to 40 times the lens’s focal length" for each setting?
Good point - I made this mistake , waiting for daylight to repeat.

---------- Post added 02-01-22 at 11:42 PM ----------

QuoteOriginally posted by c.a.m Quote
I have a couple of zoom lenses that required different AFFA settings on my K-3 II, depending on their focal lengths. For example, for my DA 20-40mm Limited, I found that the optimal AFFA calibration at 20mm was significantly different from that at 30mm and 40mm. The only setting that gave the sharpest autofocus at all focal lengths was AFFA = +2, but only when focused from infinity. So, I would simply preset the focus to infinity before each shot.

On my K-3 Mark III, I was able to find a single AFFA setting for each of my zoom lenses that produces acceptable focus across their focal length ranges.

I have a Sigma 70-200 f/2.8 HSM II, which requires an AFFA setting of -9 on my K-3 II and -7 on my K-3 Mark III. The settings produce acceptable focus at all focal lengths.

- Craig
It is K-3 Mark III, I hope I can get such result, can't wait tomorrow's daylight to do it again

---------- Post added 02-01-22 at 11:43 PM ----------

QuoteOriginally posted by zapp Quote
My DFA* differs by 2 steps between 70/135/200 mm which is visible wide open, but OK including dof …. If you did everything correct - make sample images to check - your lens just fails. Call Sigma and complain. Do you have other lens that work as expected?
Check tripod, illumination (avoid artificial light on older Pentax cameras), check target, be aware that the focus point can be larger in reality, …
It is second hand lens and I have two weeks to send it back if not OK.


A question - do you use some remote control or press buttons directly on camera?
I think remote control would be better, but I do not have one and the Smartphone app does not work for me...

Last edited by Fila; 02-01-2022 at 03:46 PM.
02-02-2022, 06:54 AM   #12
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QuoteOriginally posted by Fila Quote
I've just got second-hand lens (Sigma 70-200 f2.8) and Dot Tune session showed that 70mm starts focusing at +4 and goes all the way till +10, while 200mm goes completely into opposite direction, starts focusing at -4 and goes all the way to -10.
The ranges do not even overlap?!?

My biggest question is it bad lens, or it happens?
Aside from the lens, it could be your process and/or inconsistencies in the camera's initial (bench mark) focus using LV at various focal lengths.

When I get inconsistent results, I revert to the more traditional method of assessing focus on a slanted subject to see if I really have a problem. According to your results, you can expect to find noticeable front and back focusing depending on focal length. If you get results that can be reasonably calibrated, your inconsistent dot tune results are due to something that won't affect your photos.
02-02-2022, 07:05 AM   #13
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QuoteOriginally posted by Fila Quote
It is K-3 Mark III, I hope I can get such result, can't wait tomorrow's daylight to do it again
I have tested the Dot Tune method, and the results were quite close to my 'baseline' AFFA settings. However, Dot Tune also requires attention to detail as indicated at this post: Dot Focus microfocus adjustment - Page 3 - PentaxForums.com

- Craig
02-02-2022, 07:33 AM   #14
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QuoteOriginally posted by Fila Quote
Good point - I made this mistake , waiting for daylight to repeat.
Yes, this was fatal mistake, using distance which is 30 * focal length I get results for 200mm (-2:+9) that go in the same direction as 70mm(+4:+10), actually even better as it does not hit +10.


QuoteOriginally posted by rogerstg Quote
Aside from the lens, it could be your process and/or inconsistencies in the camera's initial (bench mark) focus using LV at various focal lengths.
I do the LV benchmark manually, I get the sharper image like this than with AF.


QuoteOriginally posted by rogerstg Quote
When I get inconsistent results, I revert to the more traditional method of assessing focus on a slanted subject to see if I really have a problem.
I was thinking of getting something like SpyderLensCal


QuoteOriginally posted by rogerstg Quote

If you get results that can be reasonably calibrated, your inconsistent dot tune results are due to something that won't affect your photos.
That's the hope



Last edited by Fila; 02-02-2022 at 07:45 AM.
02-02-2022, 08:47 AM   #15
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QuoteOriginally posted by c.a.m Quote
I have tested the Dot Tune method, and the results were quite close to my 'baseline' AFFA settings. However, Dot Tune also requires attention to detail as indicated at this post: Dot Focus microfocus adjustment - Page 3 - PentaxForums.com

- Craig
Thanks a lot for pointing this out.

QuoteOriginally posted by c.a.m Quote
  • Deciding on a reliable, positive focus confirmation (i.e., Green Hexagon ON) is somewhat subjective. While most of the AFFA settings within a range produced almost-instantaneous and robust confirmations, sometimes the Green Hex was just momentarily hesitant to illuminate.

  • Dot-Tune seems to fail when the AFFA range extends to its limit, i.e., -10 or +10. I'm not convinced by the tentative work-around suggested by the Dot-Tune creator. My Sigma 70-200mm needs an AFFA of -7 but its AFFA confirmation range would extend beyond -10. I'll need to look into this complication further.

Dot-Tune could save considerable time and tedium. Because I have characterized the AFFA behaviour of my current lenses, I could possibly use Dot-Tune for those lenses whose calibrations are 'well behaved', saving the others for my detailed approach.

- Craig

I have extracted what I can comment on::
- in DT video it is said that positive focus confirmation has to be (almost) instantaneous, but what is that almost boils down to subjective interpretation
- hitting -10 or +10 is the biggest issue for me
- It indeed saves time and tedium, I have shot 1000's of photos with my K-50 when using FocusTune ...

It would be nice to automate DT like MagicLantern did...

Last edited by Fila; 02-02-2022 at 09:06 AM.
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